Packet based communications

Abstract

This invention is applicable to packet based, rate limited radio links, such as satellite or terrestrial wireless digital communications systems. These communications networks concurrently carry time-critical traffic, such as voice or multimedia, and non time-critical traffic, such as generic data traffic, between two or more communication end points. The communication end points may be connected through a number of heterogenous networks and the end to end throughput characteristics may vary over time. A first aspect of the invention concerns a method for generating packets. In other aspects the invention concerns a computer system for use in packet based communications, a computer protocol for packet based communications and a communications packet. The invention involves determining a “time slice” packet size from the link speed and the interval of time extending between the times at which packets are selected for output from a buffer to the transmission interface. It also involves creating a network packet from frames of time-critical data generated during the interval, where the packet is synchronised to both existing timing requirements of the time-critical frames and the link speed. Then, adding non time-critical data to the network packet if its size had not exceeded the determined “time slice” packet size.

Description

TECHNICAL FIELD [0001]This invention is applicable to packet based, rate limited radio links, such as satellite or terrestrial wireless digital communications systems. These communications networks concurrently carry time-critical traffic, such as voice or multimedia, and non time-critical traffic, such as generic data traffic, between two or more communication end points. The communication end points may be connected through a number of heterogenous networks and the end to end throughput characteristics may vary over time. A first aspect of the invention concerns a method for generating packets. In other aspects the invention concerns a computer system for use in packet based communications, a computer protocol for packet based communications and a communications packet.BACKGROUND ART [0002]State of the art packet based communications systems transmit a combination of time-critical traffic, and non time-critical traffic between two or more communication end points; see FIG. 1. The ...

AI Technical Summary

Benefits of technology

[0025]Since the invention combines the time-critical and non time-critical traffic prior to including this traffic in the network packet payload, it increases the payload to header ratio.

[0028]The invention is able to increase the efficiency of packet based time-critical traffic (such as, IP telephony) in terms of the size of packet header to payload ratio.

[0029]In systems which combine multiple input streams of time-critical traffic (such as, combining a number of voice conversations in IP telephony), the invention also decreases the jitter, that is the variation in the delay of the received time critical traffic.

[0030]The invention also provides an end-to-end system which is transparent to any standard intermediate network points and which requires no additional or custom technology to be available in these points. As a result the invention is easy to implement when compared to various header compression technologies, as it can be used without any changes in the network equipment (e.g. to read compressed header information).

[0037]The invention is designed for use in burst or packet mode, but not continuous, communications systems, where the end to end throughput is not constant due to other traffic sharing one or more of the transmission links that comprise the end to end connection. The invention may improve throughput by reducing the effect of the overhead resulting from relatively large data packet headers. Each packet sent can contain both time critical and non-time critical data.

[0038]The invention may also reduce jitter time, resulting from the speed of the link, which varies from situation to situation and dynamically changes during a session. This improvement is particularly welcome in the presence of long round trip delays.

Problems solved by technology

As a result there is a high ratio of packet overhead to payload transmission.

This inefficiency is especially a problem for low bit rate communications channels.

Unless especially equipped with the appropriate decompression technology the routing equipment will not be able to read the information in the packets which have compressed headers, and this will prevent those packets from reaching their destination.

The latter method results in increased variation in the delay of the received voice frames (arising from random delays in the intermediate network points), called packet network jitter, and this reduces the perceived quality of voice in IP telephony.

The problems described above are all exacerbated when non time-critical data is to be transmitted along with VoIP packets.

However, during the time periods when a data packet is being transmitted, new voice packets entering the buffer cannot be transmitted until the current data packet has finished being transmitted.

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